1. Field of the Invention
The present invention relates to a magnetic sensing element and a process for manufacturing the same.
2. Description of the Related Art
A magnetic sensing element, for example a spin-valve type magnetic sensing element, comprises at least an antiferromagnetic layer, a pinned magnetic layer, a non-magnetic conductive layer and a free magnetic layer constituting a resistive multilayer, and a bias layer and an electrode layer are provided in both side areas of the resistive multilayer in the track width direction.
Magnetization of the pinned magnetic layer is aligned to be orthogonal to magnetization of the free magnetic layer in this spin-valve type magnetic sensing element, and the electrical resistance of the resistive multilayer changes in response to magnetization of the pinned magnetic layer when magnetization of the free magnetic layer fluctuates by being influenced by a signal magnetic field from a magnetic recording medium, thereby enabling recorded data on the magnetic recording medium to be regenerated.
FIG. 16 shows a cross section of a spin-valve type magnetic sensing element viewed from an opposed face (ABS face) to a recording medium. In the spin-valve type magnetic sensing element shown in FIG. 16, an antiferromagnetic layer 102 is formed on a gap layer 113 formed on a lower shield layer 112 in a track width direction (the X-direction in FIG. 16), and a pinned magnetic layer 103, a nonmagnetic conductive layer 104, a free magnetic layer 105 and a protective layer 106 are formed on the antiferromagnetic layer 102. A resistive multilayer 107 is composed of a laminate of these layers.
The antiferromagnetic layer 102 is formed of a platinum-manganese (Pt—Mn) alloy in this spin-valve type magnetic sensing element. The magnetization of the pinned magnetic layer 103 is pinned in a height direction (the Y-direction in FIG. 16) by an exchange coupling magnetic field generated at the interface between the antiferromagnetic layer 102 and pinned magnetic layer. The pinned magnetic layer 103 and the free magnetic layer 105 are formed of a nickel-iron (Ni—Fe) alloy, cobalt (Co), an iron-cobalt (Fe—Co) alloy or an iron-cobalt-nickel (Fe—Co—Ni) alloy. The nonmagnetic conductive layer 104 is formed of a nonmagnetic conductive material having a low electrical resistance such as copper (Cu). The resistive multilayer 107 is laminated in the Z-direction as shown in FIG. 16.
A bias underlayer 108 formed of chromium (Cr) and the like is formed on the antiferromagnetic layer 102, and a hard bias layer 109 formed of, for example, a cobalt-platinum (Co—Pt) alloy is laminated on the bias underlayer 108. The reference numeral 110 denotes an electrode formed on the hard bias layer 109.
The bias layer 109 is magnetized in the X-direction (track width direction), the magnetic direction of the free magnetic layer 105 is aligned in the same X-direction by a bias magnetic field from the bias layer 109 in the X-direction. The bias underlayer 108 is provided for improving magnetic properties of the bias magnetic field generated from the hard bias layer 109. Since the bias layer 109 also serves for aligning the magnetic direction of the free magnetic layer 105, the bias magnetic field applied from the bias layer 109 to the free magnetic layer 105 should be adjusted to its maximum.
Accordingly, terraces 103a are formed in both side areas of the pinned magnetic layer 103 located below the free magnetic layer 105 in the conventional magnetic sensing element shown in FIG. 16, in order to allow thick portions of the bias layers 109 to have direct contact with the free magnetic layer 105.
Since the thick portion of the hard bias layer 109 makes direct contact with the free magnetic layer 105 in the structure shown in FIG. 16, the bias magnetic field may be effectively applied from the hard bias layer 109 to the free magnetic layer 105. However, desired magnetic characteristics may be not always sufficient.
Technical considerations of the phenomena described above will be presented hereinafter. While the bias underlayer 108 is provided in order to improve magnetic properties of the bias layer 109, no bias underlayer 108 is formed under the hard bias layer 109 on the terrace 103a when the terrace 103a of the pinned magnetic layer 103 is noticed.
The hard bias layer 109 is directly bonded to the free magnetic layer 105 on the terrace 103a of the pinned magnetic layer 103, and a bias magnetic field is applied to the free magnetic layer 105 from the bias layer 109 due to the bias magnetic field generated at the interface between them. Consequently, improvements of the magnetic properties of the hard bias layer 109 on the terrace 103a of the pinned magnetic layer 103, where the bias magnetic field is generated, should be particularly emphasized.
However, the expected characteristics cannot be obtained in the conventional example shown in FIG. 16, because no bias underlayer 108, which is to be formed corresponding to the portion where the bias magnetic field is generated, is formed on the terrace 103a of the pinned magnetic layer 103, and the magnetic properties are not improved due to deteriorated coercive force of the hard bias layer 109 at the portion where the bias magnetic field is generated.
FIG. 30 is a cross section of a conventional spin-valve type magnetoresistive element viewed from an opposed face (ABS face) to a recording medium. In the spin-valve type magnetoresistive element shown in the drawing (a first comparative example), an antiferromagnetic layer 102 formed on an underlayer 101 is elongated in a track with Tw direction (the X-direction), and the antiferromagnetic layer 102 at the center of the track width region (referred to as a center in the X-direction for convenience' sake) is projected with an elevation denoted by d1. A pinned magnetic layer 103, a nonmagnetic conductive layer 104, a free magnetic layer 105 and a protective layer 106 are formed on the projected antiferromagnetic layer 102, forming a multilayer 107 comprising the layers from the underlayer 101 through the protective layer 106.
The antiferromagnetic layer 102 is formed of a platinum-manganese (Pt—Mn) alloy layer in the spin-valve type thin film element in a second comparative example. The magnetization of the pinned magnetic layer 103 is pinned in the height direction (Y-direction) due to an exchange coupling magnetic field generated at the interface between the antiferromagnetic layer 102 and pinned magnetic layer. The pinned magnetic layer 103 and the free magnetic layer 105 are formed of a nickel-iron (Ni—Fe) alloy, cobalt, an iron-cobalt (Fe—Co) alloy, an iron-cobalt-nickel (Fe—Co—Ni) alloy and the like. The nonmagnetic conductive layer 104 is formed of a nonmagnetic conductive material having a low electrical resistance such as copper (Cu). The layers are laminated in the Z-direction.
A bias underlayer 108 formed of chromium and the like that serve as buffer layer and orientation layer is formed on each side face from the antiferromagnetic layer 102, formed by being elongated in the X-direction, through side faces on the multilayer 107. A hard bias layer (hard magnetic layer) 109 formed of, for example, a cobalt-platinum (Co—Pt) alloy is laminated on each bias underlayer 108.
The hard bias layer 109 is magnetized in the X-direction (track width direction), and the magnetization of the free magnetic layer 105 is aligned in the same X-direction due to a bias magnetic field in the X-direction from the hard bias layer 109. The hard bias layer 108 enhances the bias magnetic field generated from the hard bas layer 109.
An electrode layer 110 is laminated on the hard bias layer 109 with chromium (Cr), gold (Au), tantalum (Ta) or tungsten (W).
The bias magnetic field generated from the hard bias layer 109 is amplified by forming the bias underlayer 108 from the antiferromagnetic layer 102 through each side face on the multilayer 107. While the hard bias layer 109 is provided in order to align the magnetic direction of the free magnetic layer 105, it is necessary to increase the bias magnetic field generated from the hard bias layer (hard magnetic layer) 109 in the vicinity of the free magnetic layer 105.
In the spin-valve type thin film element having the construction as described above, or having a construction in which the bias underlayer 108 and the hard bias layer 109 are laminated on each antiferromagnetic layer 102 at each side of the central region of the antiferromagnetic layer 102, crystals of the hard bias layer 109 on the antiferromagnetic layer 102 tend to be oriented in a non-preferential direction, thereby arising a trouble by which the magnetic property of the hard bias layer is deteriorated to cause linearity and stability of regenerated waveform to be deteriorated.
In other words, while biasing characteristics of the hard bias layer 109 are strongly dependent on the crystal orientation of the bias underlayer 108 formed during deposition thereof, the crystal orientation of the bias underlayer 108, for example a Cr layer, is conjectured to be changed from its intrinsic crystal orientation by being restricted to the crystal orientation of the antiferromagnetic layer 102 due to the lamination structure with the antiferromagnetic layer 102a located just under the bias underlayer. As a result, the coercive force of the hard bias layer 109 laminated on the bias underlayer 108 is decreased.
Therefore, in the spin-valve type thin film element shown in FIG. 29 (a third comparative example), a multilayer 107 formed on a lower shield layer 112 and lower gap layer 113 is excessively milled before depositing an electrode layer 110 and a hard bias layer 109. In other words, the portions of the antiferromagnetic layer 102 elongating to both sides of the multilayer 107 as well as a part of the lower gap layer 113 located just under the antiferromagnetic layer are removed by over-etching, followed by laminating a bias underlayer 108.
Although good hard bias characteristics may be obtained in the spin-valve type thin film element having the construction as described above, the bias layer 109 is tapered toward the side face of the multilayer 107 (the hard bias layer 109 is thinned in the vicinity of a free magnetic layer 105). Consequently, the hard bias layer 109 cannot be formed with a desired thickness in the vicinity of each side face of the free magnetic layer 105, making it difficult to effectively apply a bias magnetic field generated from the hard bias layer (hard magnetic layer) 109 in the vicinity of the free magnetic layer 105.
Accordingly, it is preferable to remove at least the entire multilayer 107 by milling at both side areas of the multilayer 107, or to apply a more deeper ion-milling (over-etching) of the lower gap layer 113. However, when the both sides of the multilayer are completely removed or a more deeper ion-milling is applied to the lower gap layer, the hard bias layer 109 becomes more tapered to make it difficult to apply an effective magnitude of the bias magnetic layer to the free magnetic layer 105, thereby resulting in deficiency of linearity and stability of the regenerated waveform.